What is the weight of a man with a mass of 80 kg on Earth and the moon?

Let us make sure we understand mass and weight are not the same thing. 80 kg of mass is not the same thing as 80 N of weight. To calculate weight, we use Newton's 2nd Law of Motion, which gives us the formula "Force = mass x acceleration". We would take the mass given, 80 kg, and multiply it times the acceleration of Earth's downward pull on that mass, 9.8 m/s/s.

784 N = 80 kg x 9.8 m/s/s

So the weight on Earth is 784 newtons.

Now the gravitational attraction of the moon is about 1/6 that of the Earth, or about 17%. To calculate the weight on the moon, simply multiply 784 N times .17, or 17% in decimal form: